Fix metadata rendering issue

[narasaka]

Description

Prior to this commit, the printed metadata was wrapped/formatted incorrectly when running mcap list metadata. This commit fixes it by removing the pretty json format – making the metadata column print only 1 line.

[wkalt]

@narasaka this still looks misaligned:

[~/data/mcap] $ mcap list metadata gps.mcap
name         offset   length  metadata
my-metadata  1255462  56      {
                             "biz": "baz",
                             "foo": "bar"
                           }

what do you think about just putting it all on one line like in mcap list channels?